THE NONMETALLIC MINERALS. 369 



in the form of nodular concretions of a size varying from that of an 

 egg to a cocoanut, closely packed together and cemented by a black 

 slaty matrix. The concretions have often a black highly polished 

 appearance, due to the presence of graphite, but owing to the pres- 

 ence of oxidizing pyrite they sometimes become rusty brown. The 

 concretions carry from 60 to 69 per cent of phosphate of lime; the 

 matrix is also phosphatic. The phosphate beds are highly tilted and 

 are overlaid by gray shales with fossilized echinoderms and underlaid 

 by dark crystalline limestone, which also contains from 15 to 20 per 

 cent of phosphatic material. Davies regards the deposit as an old sea 

 bottom "on which the phosphatic matter of Cretaceous and Molluscan 

 life was precipitated and stored during a long period, while certain 

 marine plants may also have contributed their share of phosphatic 

 matter. He thinks it also as possible that, as in the Lauren tian deposits, 

 the water of the sea may have contained phosphatic matter in solution, 

 to be deposited independently of organic agencies. 



These phosphated beds are mined at Berwin, where an average pro- 

 duction over a space of 360 fathoms was 2 tons 10 hundredweight of 

 phosphate per fathom, of an average strength of 46 per cent. 



The nodules average from 45 to 55 per cent of phosphate of lime. 



Amorphous nodular phosphates also occur in both the Upper and 

 Lower Greensands of the Cretaceous and in Tertiary deposits. Those 

 of the upper beds have been mined in Cambridgeshire and Bedford- 

 shire. The phosphatic material occurs in the form of shell casts, 

 fossils, and nodules, of a black or dark-brown color, of varying hard- 

 ness, embedded in a sand consisting of siliceous and calcareous matter 

 as well as phosphatic and glauconitic grains. The average composi- 

 tion shows from 40 to 50 per cent of phosphate of lime. The thick- 

 ness of the nodule-bearing bed is rarely over a foot. The nodules of 

 the Lower Greensands differ from those of the Upper in many details, 

 the more important being their lower percentages of phosphate of 

 lime (from 40 to 50 per cent). They occur in a bed of siliceous sand 

 which itself is not phosphatic. The Tertiary phosphates reach their 

 best development in the county of Suffolk, where they are found at 

 the base of the Coralline and Red Crog groups and immediately over- 

 lying the London clays. The beds consist of a "mass of phosphatic 

 nodules and shell casts, siliceous pebbles, teeth of cretaceans and sharks, 

 and many mammal bones, besides occasional fragments of Lower 

 Greensand chert, granite, and chalk flints." The nodules vary in both 

 quality and quantity. They are at times of a compact and brittle 

 nature, while at others they are tough and siliceous. They average 

 about 53 per cent phosphate of lime and 13 per cent phosphate of iron. 



France. Phosphates of the nodular type occur in beds of Cretaceous 

 age in the provinces of Ardennes and Meuse, and to a less extent in 

 others in northern France; in the department of Cote d'Or, and along 

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